A conductive resin composition such as a conductive paste, a conductive paint, and a conductive adhesive has conventionally been employed for various applications such as electronic components and electronic circuits. Granular or flaky silver (Ag) particles and copper (Cu) particles have been known as a conductive filler used for such a conductive resin composition. Though Ag is excellent in conductivity, it is disadvantageously expensive. Cu is prone to oxidation and low in corrosion resistance, and hence it disadvantageously cannot maintain conductivity for a long period of time.
In order to address this, Japanese Patent Laying-Open No. 2008-111175 (PTD 1), Japanese Patent Laying-Open No. 2004-52044 (PTD 2), and Japanese Patent Laying-Open No. 2006-161081 (PTD 3) each have proposed a conductive filler in which surfaces of Cu particles are coated with Ag. This conductive filler is characterized by excellent conductivity, corrosion resistance, and moisture resistance. Cu, however, is high in specific gravity. Therefore, when Cu particles are employed as core particles, the conductive filler tends to precipitate in a conductive resin composition and handleability (ease in handling) thereof is disadvantageously low.
A conductive filler in which a surface of a resin low in specific gravity is coated with Ag has been developed as a technique for solving the problem of specific gravity. A resin itself to be core particles, however, has no conductivity. Therefore, in order to obtain high conductivity of this conductive filler, an amount of use of Ag should be increased, which results in high manufacturing cost.
In order to address the various problems described above, aluminum (Al) particles can be exemplified as core particles which are inexpensive, low in specific gravity, and conductive. For example, Japanese Patent Laying-Open No. 2010-53436 (PTD 4) discloses a conductive filler in which surfaces of Al particles are coated with Ag.